1. Field of the Invention
The present invention generally relates to storage area networks. Particularly, the present invention relates to a method and a system for operating a storage area network in a server environment in which multiple servers share one Fibre Channel adapter.
2. Description of the Related Art
Fibre channel is a high speed, full-duplex, serial communications technology used to interconnect input/output (I/O) devices and host systems that can be separated by tens of kilometers. It incorporates the best features of traditional I/O interfaces, like throughput and reliability found in SCSI and PCI, with the best features of networking interfaces, like connectivity and scalability found in Ethernet and Token Ring. It provides a transport mechanism for the delivery of existing commands, and provides an architecture that achieves high performance by allowing a significant amount of processing to be performed in hardware. It can operate with legacy protocols and drivers like SCSI and IP, enabling it to be introduced easily into existing infrastructures.
Fibre channel transfers information between the sources and the users of the information. This information can include commands, controls, files, graphics, video and sound. Fibre channel connections are established between Fibre channel ports residing in I/O devices, host systems, and the network interconnecting them. The network consists of elements like switches, hubs, bridges and repeaters that are used to interconnect the Fibre Channel ports.
There are three Fibre Channel topologies defined in the Fibre Channel architecture. These are Point-to-Point, Switched Fabric and Arbitrated Loop.
Fibre channel switches (or switched fabrics) also include functions commonly called Zoning. These functions allow the user to partition the switch ports into port groups. The ports within a port group, or zone, can only communicate with other ports in the same port group (zone). By using zoning, the I/O from one group of hosts and devices can be completely separated from that of any other group, thus preventing the possibility of any interference between the groups.
This is also referred to as “soft zoning”. The way this soft zoning works is that the user assigns nodes to a zone according to the node's World Wide Name—either the World Wide Port Name (WWPN) or the World Wide Node Name (WWNN). The name server captures this information, which is a function embedded within the switch. Then, whenever a port communicates with the name server to find out to which nodes it is allowed to connect, the name server will respond only with the nodes that are within that port's zone.
Since the standard Fibre Channel device drivers do communicate with the name server in this manner, this type of zoning is adequate for most situations. However, it is possible that a device driver could be designed that would attempt to access nodes not in its list of allowed connections. If this occurred, the switch would neither prevent nor detect the violation.
In order to prevent this case, switches also optionally implement a mechanism called “hard zoning” in addition to soft zoning, where the switch network decides based solely on source and destination address of each frame if this frame is allowed to be transported.
Fiber channel Storage Area Networks (SANs) are networks that connect storage devices to host servers. They are built upon the Fibre Channel technology as a networking infrastructure. What differentiates SANs from previous interconnection schemes is the basic concept that all (or mostly all) of the storage can be consolidated in one large “storage area” that allows centralized (simplified) management in addition to any-to-any connectivity between host servers and the storage.
Fibre channel SANs have the potential to allow the interconnection of open systems and storage (i.e., non-zSeries) in the same network as zSeries systems and storage. This is possible because the protocols for both open attachment and zSeries attachment are being mapped to the FC-4 layer of the Fibre Channel architecture.
In Fibre Channel attachments, LUNs have an affinity to the host's Fibre Channel adapter (via the adapter's World Wide Unique Identifier, a.k.a. the World Wide Port Name), independent of which ESS (IBM Enterprise Storage Server) Fibre Channel port the host is attached to. Therefore, in a switched fabric configuration where a single Fibre Channel host can have access to multiple Fibre Channel ports on the ESS, the sets of LUNs, which may be accessed by the Fibre Channel host, are the same on each of the ESS ports.
One result of this implementation is that with Fibre Channel, unlike in SCSI, hosts that are attached to ESS via a fabric to the same Fibre Channel port may not be able to “see” the same LUNs, since the LUN masking can be different for each Fibre Channel host. In other words, each ESS can define which host has access to which LUN.
Another method is to create zones in the switch such that each Fibre Channel port from each host is constrained to attach to one Fibre Channel port on the ESS, thereby allowing the host to see the LUNs via one path only.
Details of the Fibre Channel specification are shown in the following standards: Fibre Channel Physical and Signaling Interface (FC-PH), ANSI X3.230-1994; Fibre Channel Second Generation Physical Interface (FC-PH-2), ANSI X3.297-1997; Fibre Channel Third Generation Physical Interface (FC-PH-3), ANSI X3.303-199x, Revision 9.4 and Fibre Channel Arbitrated Loop (FC-AL), ANSI X3.272-1996. Further relevant standards are FC-FS, FC-GS-3.
Further information concerning the Fibre Channel is disclosed in The Fibre Channel Consultant—A Comprehensive Introduction (Robert W. Kembel, 1998) and The Fibre Channel Consultant—Arbitrated Loop (Robert W. Kembel, 1996).
EP 1 115 225 A2, by Barry Stanley Barnett et al., assigned to International Business Machines Corporation, Armonk, N.Y., US, filed Dec. 22, 2000, published Jul. 11, 2001, “Method and system for end-to-end problem determination and fault isolation for storage area networks” discloses a method and system for problem determination and fault isolation in a storage area network (SAN). A complex configuration of multi-vendor host systems, FC switches, and storage peripherals are connected in a SAN via a communications architecture (CA). A communications architecture element (CAE) is a network-connected device that has successfully registered with a communications architecture manager (CAM) on a host computer via a network service protocol, and the CAM contains problem determination (PD) functionality for the SAN and maintains a SAN PD information table (SPDIT). The CA comprises all network-connected elements capable of communicating information stored in the SPDIT. The CAM uses a SAN topology map and the SPDIT are used to create a SAN diagnostic table (SDT). A failing component in a particular device may generate errors that cause devices along the same network connection path to generate errors. As the CAM receives error packets or error messages, the errors are stored in the SDT, and each error is analyzed by temporally and spatially comparing the error with other errors in the SDT. If a CAE is determined to be a candidate for generating the error, then the CAE is reported for replacement if possible.
US 2001/0054093 A1, by Sawao Iwatani, Kawasaki, Japan, filed Feb. 9, 2001, published Dec. 20, 2001, “Storage area network management system, method, and computer-readable medium” discloses an integrated management mechanism of a storage area network (SAN) integrating and managing a traditionally dispersed security system from a single source and automates security management in the SAN. The integrated management mechanism integrates and manages the SAN, and is configured so that access relationships of the host computers and the storage devices of the SAN are managed using the integrated management mechanism. An access path on the integrated management mechanism, including a region of the storage devices to which access is attempted from the host computer, the fiber channel adapters used when accessing that storage, and the host bus adapters (HBA) are configured. Based on the access path information configured, the integrated management mechanism establishes respective storage settings, zoning settings, and accessible region permissions for a SAN management mechanism of the host computer, a zoning settings mechanism of the switch, and a storage management mechanism of the storage device.